1. Field of the Invention
This invention relates to a novel recording liquid, particularly to a recording liquid suitable for a recording system in which recording is performed by permitting a recording liquid to be discharged through a fine discharging outlet (discharging orifice) provided at a recording head and fly as droplets.
2. Description of the Prior Art
For the writing tools (fountain pens, felt pens, etc.) to perform recording on a recording sheet such as paper of the prior art, various types of ink has been used wherein dyes are dissolved in water or other organic solvent.
On the other hand, in the so-called ink jet recording system wherein the liquid contained in a recording head is discharged by vibration by means of a piezo-vibrating element or electrostatic attracting force by application of a high voltage thereby to effect recording, compositions having various dyes dissolved in water or organic solvents have been known to be used. However, as compared with ink for stationery such as fountain pens or felt pens in general, the recording liquid for ink jet recording is used in more severe conditions in a large number of characteristics.
Such an ink jet recording method performs recording by permitting droplets of a recording liquid called as ink to fly and to be attached onto a recording sheet. Such a recording liquid is composed basically of a recording agent (dyes or pigments are used) and a liquid medium for dispersing said agent (water or various organic solvents or mixtures thereof are used), and may also contain various additives, if desired.
For such recording methods, there are various systems depending on the method of generating droplets and the method of controlling the flying direction of the droplets. FIG. 1 shows an example of such systems.
More specifically, the device shown in FIG. 1 gives recording signals to the recording head having a piezo-vibrating element and permits droplets of a recording liquid to be generated responding to said signals thereby to effect recording. In FIG. 1, 1 is a recording head and has a piezo-vibrating element 2a, a vibrating plate 2b, an inlet for recording liquid 3, a liquid chamber 4 within the head and a discharging outlet (discharging orifice) 5. Into the liquid chamber 4, a recording liquid 7 stored in a reservoir tank 6 is fed through a feed pipe 8. In the course of the feed pipe, an intermediate treating means 9 such as pump or filter may sometimes be provided. And on the piezo-vibrating element 2a, a signal transduced from the recording signal 8 to pulse by means of the signal processing means 10 (e.g. pulse transducer) is applied, and pressure change corresponding to said signal will occur on the recording liquid within the liquid chamber 4. As a result, the recording liquid 7 is discharged through the orifice 5 as the droplet 11 to effect recording on the surface of the recording sheet 12.
Other than the device as described above, various types of devices have been known. For example, as shown in FIG. 2, the liquid chamber 4 is made like a nozzle as a modification of FIG. 1, and a cylindrical piezo-vibrating element is arranged at the peripheral portion thereof (the mechanism of this device for generation of droplets is essentially the same as the device shown in FIG. 1). There is also a device in which electrically charged droplets are continuously generated, and a part of said droplets are used for recording. Alternatively, also known is a device in which heat energy responding to recording signal is given to the recording liquid within the chamber of the recording head to generate droplets by said energy.
One example of such a device is shown in FIG. 3A, FIG. 3B, FIG. 3C and FIG. 4.
The head 13 is obtained by bonding a glass, ceramic or plastic plate and the like having groove 14 for passing ink with a heat generating head 15 (in the drawings, thin film head is shown, but it is not limited thereto). The heat generating head 15 is composed of a protective film 16 formed of silicon oxide, etc., aluminum electrodes 17-1 and 17-2, a heat generating resistor layer 18 formed of nickel-chromium, etc., a heat accumulating layer 19 and a substrate 20 having good heat releasing property such as alumina, etc.
The ink 21 has come to the discharging orifice 22 and forms a meniscus 23 under a pressure P.
On application of an electrical signal on electrodes 17-1 and 17-2, the region shown by n of the heat generating head 15 will generate heat abruptly and bubbles of the ink 21 in contact with said region are generated, whereby the meniscus is protruded by the pressure of the bubbles discharging the ink 21 through the orifice 22 as small recording droplets, which then fly toward the recording sheet. FIG. 4 shows a perspective view of the appearance of a multi-head in which a number of the heads shown in FIG. 3A are juxtaposed. Said multi-head is made by bonding a glass plate 27 having a multi-groove 26 with the same heat generating head 28 as described with reference to FIG. 3A.
In the above drawings, FIG. 3A is a sectional view of the head 13 taken along the ink pathway, and FIG. 3B is a sectional view of FIG. 3A taken along the line A - B.
In the prior art, as the recording liquid of this kind, various solutions or dispersions having various dyes or pigments dispersed in aqueous or non-aqueous solvents have been known, as disclosed in, for example, Japanese Patent Publication Nos. 8361/1975, 40484/1976, 13126/1977 and 13127/1977, and Japanese Laid-open Patent Publication No. 95008/1975. Desired characteristics for the recording liquid of this kind are:
(1) to have liquid physical properties (viscosity, surface tension, electroconductivity, etc.) matched with the discharging conditions (voltage for driving piezoelectric elements, driving frequency, shape and material of orifice, orifice diameter, etc.); PA1 (2) to be stable during storage over a long term without clogging of minute discharging orifice or capillary pores; PA1 (3) to be rapidly fixed onto a recording sheet (paper, film, etc.) and smooth around the dot with little blurring; PA1 (4) to be capable of giving a printed image which is clear in tone and high in density; PA1 (5) to be capable of giving a printed image excellent in water resistance and light resistance. PA1 (6) not to corrode surrounding materials (vessel, connecting tube, sealant, etc.); and PA1 (7) to be excellent in safety being free from odor, toxicity, flammability, etc. PA1 (a) either one or both of polyethylene glycol and polyethylene glycol monomethyl ether, PA1 (b) either one or both of diethylene glycol and sulfolane; PA1 (c) either one or both of N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone; and PA1 (d) water. PA1 (a) either one or both of polyethylene glycol and polyethylene glycol monomethyl ether, PA1 (b) either one or both of diethylene glycol and sulfolane; PA1 (c) either one or both of N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone; and PA1 (d) water. PA1 (a) either one or both of polyethylene glycol and polyethylene glycol monomethyl ether, PA1 (b) either one or both of diethylene glycol and sulfolane; PA1 (c) either one or both of N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone; and PA1 (d) water.